The invention relates generally to radiographic detectors for diagnostic imaging, and more particularly to large area detectors for high flux rate imaging, such as in computed tomography (CT) applications.
Radiographic imaging systems, such as X-ray and computed tomography (CT) have been employed for observing, in real time, interior aspects of an object. Typically, the imaging systems include an X-ray source that is configured to emit X-rays toward an object of interest, such as a patient or a piece of luggage. A detecting device, such as an array of radiation detectors, is positioned on the other side of the object and is configured to detect the X-rays transmitted through the object.
Conventional CT and other radiographic imaging systems utilize detectors that convert radiographic energy into current signals that are integrated over a time period, then measured and ultimately digitized. A drawback of such detectors however is their inability to count at the X-ray photon flux rates typically encountered with conventional CT systems. Additionally, conventional detectors also lack the ability to track the energy of incident x-rays. For example, photon counting direct conversion detectors are known to suffer from decreased detection quantum efficiency (DQE) at high count rates mainly due to detector pile-up. Further, very high X-ray photon flux rate has been known to cause pile-up and polarization that ultimately leads to detector saturation. In other words, these detectors typically saturate at relatively low X-ray flux level thresholds. Above these thresholds, the detector response is not predictable or has degraded dose utilization. That is, once a pixel is saturated (corresponding to a bright spot in the generated signal), additional radiation will not produce useful detail in the image.
Previously conceived solutions to enable photon counting at high X-ray flux rates include employing pixels having a relatively small size to achieve higher spatial resolution and reduce flux rate sensitivity. Unfortunately, this reduction in the pixel size results in increased cost.
Additionally, applications such as medical and industrial imaging, NDE, security, baggage scanning, astrophysics and medicine may entail the use of larger coverage detectors that encompass large areas. In the field of medical diagnostics, such as, but not limited to, computed tomography (CT), ultrasound and mammography, it may be desirable to employ larger detectors to facilitate acquisition of image data from a large portion of the anatomy in a single gantry rotation thereby enhancing image quality.
Previously conceived solutions to obtaining wider coverage involved increasing the number of rows of detector elements. Arrays of detectors have also been utilized to circumvent the problems associated with employing single large area detectors. The X-Y plane may be employed for assembling the detectors arrays to facilitate the construction of large area detectors arrays. However, such arrays can be very dense and necessitate a large quantity of control and amplifier electronics to drive the individual detectors of the array. Presently, the control and amplifier electronics employed to drive the individual detectors are also positioned in the X-Y plane resulting in a large footprint and potentially, gaps in the detector area due to the need to locate electronics in or adjacent to the detector. Furthermore, the density of input/output (I/O) required for coupling the individual detectors with the associated electronics may be very high. Also, the density of I/O may be too large for traditional interconnect strategies to handle. Presently, the interconnect lengths required to couple the detector elements to the electronic device are very long. It would be desirable to minimize interconnect lengths in order to circumvent problems associated with longer interconnect lengths, such as, effects of capacitance, and degraded signal quality.
There is therefore a need for a design of a detector that does not saturate at the X-ray photon flux rates typically found in conventional radiographic systems. In particular, there is a significant need for a design that advantageously enhances the flux rate in detectors that will allow photon counting with energy discrimination in medical and industrial applications that are heretofore unmanageable because either the flux rate or the dynamic range requirements are too high. Additionally, there is a particular need to assemble large area detector arrays in order to circumvent associated problems, such as, complexities and costs associated with manufacturing. Furthermore, it would be desirable to position the associated electronics in close proximity to the individual detector elements of the detector array in order to minimize system size, complexity, interconnect lengths and enhance the performance of the detector arrays.